Seal ring

Abstract

A seal ring is provided which allows the interior of a cylinder 1 of a screw extruder to be maintained at elevated temperature and elevated pressure, thus suppressing a variation in the pressure in the cylinder 1 . In a special seal ring 300 attached to a screw shaft 7 in the cylinder of the screw extruder so as to be rotatable integrally with the screw shaft 7 , thus restraining a material to be treated from being fed from upstream to downstream in the cylinder, a lead groove 317 extending in an axial direction of the shaft 7 is formed in an outer circumferential surface 316 opposing with a predetermined gap to an inner circumferential surface 1 a of the cylinder. The lead groove 317 serves to disturb the flow of the material to be treated passing between the outer circumferential surface 316 and the inner wall surface 1 a of the cylinder 1 to complex the flow. This stabilizes feeding resistance to suppress a variation in the pressure in the cylinder 1.

The invention claimed is: 
     
       1. A seal ring attached to a screw shaft in a cylinder of a screw extruder so as to be rotatable integrally with the screw shaft, thus restraining a material to be treated from being fed from upstream to downstream in the cylinder, the seal ring comprising:
 a shaft portion with a shaft hole through which the screw shaft is inserted, 
 a circular expanded diameter portion formed by expanding a diameter of the shaft portion, the expanded diameter portion comprising an outer circumferential surface opposing an inner wall surface of the cylinder with a predetermined gap therebetween; 
 a lead groove formed in the outer circumferential surface and extending in an axial direction of the screw shaft; and 
 the expanded diameter portion further comprising a front surface at an upstream end of the expanded diameter portion as viewed in a feeding direction, and a stepped portion formed at an edge portion between the outer circumferential surface and the front surface. 
 
     
     
       2. The seal ring according to  claim 1 , further comprising a recessed portion formed in the outer circumferential surface and which is open toward the front surface so as to have an upstream side face the feeding direction, the recessed portion being narrower on a downstream side thereof than on the upstream side thereof in the feeding direction, the downstream side of the recessed portion communicating with an upstream portion of the lead groove. 
     
     
       3. The seal ring according to  claim 2 , wherein the recessed portion has the same depth as that of the lead groove and a semicircular shape projecting downstream of a front surface of the expanded diameter portion in the feeding direction. 
     
     
       4. The seal ring according to  claim 1 , further comprising a circumferential groove formed in the outer circumferential surface of the expanded diameter portion and extending along a circumferential direction of the outer circumferential surface. 
     
     
       5. The seal ring according to  claim 4 , wherein a plurality of circumferential grooves are formed at predetermined intervals spaced apart in the feeding direction. 
     
     
       6. The seal ring according to  claim 4 , wherein each of the circumferential grooves comprises a recessed circular arc-shaped recessed curved surface portion located on an upstream side thereof in the feeding direction and having a cross-sectional shape with a predetermined radius of curvature, and
 the circumferential groove further comprises an inclined tapered portion located on a downstream side of the circumferential groove in the feeding direction and having a cross-sectional shape gradually inclined at a predetermined inclination angle from the recessed curved surface toward a radially outer side of the expanded diameter portion toward the downstream side in the feeding direction. 
 
     
     
       7. The seal ring according to  claim 1 , wherein the lead groove has a cross section shaped like a substantially squared U-shaped groove. 
     
     
       8. The seal ring according to  claim 1 , wherein the lead groove has a cross section shaped like a substantially U-shaped or V-shaped groove in a region from the outer circumferential surface toward a bottom of the lead groove, the substantially U-shaped or V-shaped groove being obtained by cutting the outer circumferential surface toward the rearward side of the rotating direction.